Late-glacial and Holocene vegetation dynamics at various altitudes in the Ellero Valley, Maritime Alps, nortwestern Italy
Résumé
This study aims to reconstruct the variations of the vegetation zonation in the Ellero Valley (Maritime Alps, Italy) since the Late-glacial. Based on the analysis of percentages of dominant pollen taxa (Pinus, Abies, Fagus, deciduous Quercus, Artemisia, Poaceae) in sediment cores from three peat bogs at different altitudes (Pian Marchisio, 1624 m, Rifugio Mondovì, 1760 m and Torbiera del Biecai, 1920 m) this study offers an interpretation of pollen percentages in terms of vegetation cover. The correlation of the pollen zones in the three diagrams is validated by correspondence analysis and supported by twelve 14C (AMS) dates. The Oldest and the Younger Dryas are characterized by steppe vegetation dominated by Artemisia. The Bølling/Allerød warming which separates the Oldest and the Younger Dryas is characterized by a Pinus shift. Pine and birch forests develop at 1900 m asl at the beginning of the Holocene. The fir-wood colonization of the mountainous and subalpine belts is dated 9540-9406 cal. years BP and follows these first phases. Fir development and the arrival of beech are dated 8767-8543 cal. years BP: beech is recorded about 1000-2000 years earlier than in the adjacent regions. It develops between 1100 and 1600 m asl, forming a vegetation belt between the oak-wood in the lowland and the subalpine fir-wood. Fir decreases from 2792-2459 cal. years BP. Since this period, a beech-fir mountainous belt has been present at 1700 m. Both the suppression of the fir-forest and the lowering of the upper beech-wood limit to 1500 m are due to human activity during the last millennium.